286 research outputs found
Plane-wave based electronic structure calculations for correlated materials using dynamical mean-field theory and projected local orbitals
The description of realistic strongly correlated systems has recently
advanced through the combination of density functional theory in the local
density approximation (LDA) and dynamical mean field theory (DMFT). This
LDA+DMFT method is able to treat both strongly correlated insulators and
metals. Several interfaces between LDA and DMFT have been used, such as (N-th
order) Linear Muffin Tin Orbitals or Maximally localized Wannier Functions.
Such schemes are however either complex in use or additional simplifications
are often performed (i.e., the atomic sphere approximation). We present an
alternative implementation of LDA+DMFT, which keeps the precision of the
Wannier implementation, but which is lighter. It relies on the projection of
localized orbitals onto a restricted set of Kohn-Sham states to define the
correlated subspace. The method is implemented within the Projector Augmented
Wave (PAW) and within the Mixed Basis Pseudopotential (MBPP) frameworks. This
opens the way to electronic structure calculations within LDA+DMFT for more
complex structures with the precision of an all-electron method. We present an
application to two correlated systems, namely SrVO3 and beta-NiS (a
charge-transfer material), including ligand states in the basis-set. The
results are compared to calculations done with Maximally Localized Wannier
functions, and the physical features appearing in the orbitally resolved
spectral functions are discussed.Comment: 15 pages, 17 figure
High-Resolution Infrared Imaging of Herschel 36 SE: A Showcase for the Influence of Massive Stars in Cluster Environments
We present high-resolution infrared imaging of the massive star-forming region around the O-star Herschel 36. Special emphasis is given to a compact infrared source at 0".25 southeast of the star. The infrared source, hereafter Her 36 SE, is extended in the broad-band images, but features spatially unresolved Br gamma line emission. The line-emission source coincides in position with the previous HST detections in H alpha and the 2 cm radio continuum emission detected by VLA interferometry. We propose that the infrared source Her 36 SE harbors an early B-type star, deeply embedded in a dusty cloud. The fan shape of the cloud with Herschel 36 at its apex, though, manifests direct and ongoing destructive influence of the O7V star on Her 36 SE
The Loss of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Caused by 24-Hour Rain Treatment Fully Explains the Decrease in the Photosynthetic Rate in Bean Leaves
Recommended from our members
Low density molecular gas in the galaxy
The distributions and physical conditions in molecular gas in the interstellar medium have been investigated in both the Galaxy and towards external galaxies. For example, Galactic plane surveys in the CO J =1-0 line with the Columbia 1.2-m telescope and with the Five College Radio Astronomy Observatory (FCRAO) 14-m telescopes have been able to trace spiral arms more clearly than HI surveys have been able to reveal, and indicate that most of molecular mass is contained in Giant Molecular Clouds (GMCs). Extensive maps of the whole Milky Way showed two prominent features, the 4-kpc molecular ring and the Galactic center. The physical conditions in the Galaxy have been studied by comparing the intensity of CO J =1-0 line with those of other lines, e.g., 13CO J =1-0, higher J transitions of CO, and dense gas tracers such as HCO+, CS, and HCN.
Previous studies were however strongly biased towards regions where CO emission was known to be intense. The radial distribution of molecular hydrogen shows that most of the H2 gas which is indirectly traced by observations of its associated CO emission, originates from the inner Galaxy (Dame 1993). Extending outwards from a galacto-centric distance of ~7 kpc, the H2 mass surface density decreases dramatically, and HI dominates over H2 in the outer Galaxy. What are physical conditions of molecular gas where the CO emission is relatively weak, and can we really trace all of the molecular gas through obervations of CO? These kinds of problems have not been solved yet, but are addressed in our study
The LAOG-Planet Imaging Surveys
With the development of high contrast imaging techniques and infrared
detectors, vast efforts have been devoted during the past decade to detect and
characterize lighter, cooler and closer companions to nearby stars, and
ultimately image new planetary systems. Complementary to other observing
techniques (radial velocity, transit, micro-lensing, pulsar-timing), this
approach has opened a new astrophysical window to study the physical properties
and the formation mechanisms of brown dwarfs and planets. I here will briefly
present the observing challenge, the different observing techniques, strategies
and samples of current exoplanet imaging searches that have been selected in
the context of the LAOG-Planet Imaging Surveys. I will finally describe the
most recent results that led to the discovery of giant planets probably formed
like the ones of our solar system, offering exciting and attractive
perspectives for the future generation of deep imaging instruments.Comment: 6 pages, 5 figures, Invited talk of "Exoplanets and disks: their
formation and diversity" conference, 9-12 March 200
X-Ray Magnetic Circular Dichroism at the K edge of Mn3GaC
We theoretically investigate the origin of the x-ray magnetic circular
dichroism (XMCD) spectra at the K edges of Mn and Ga in the ferromagnetic phase
of Mn3GaC on the basis of an ab initio calculation. Taking account of the
spin-orbit interaction in the LDA scheme, we obtain the XMCD spectra in
excellent agreement with the recent experiment. We have analyzed the origin of
each structure, and thus elucidated the mechanism of inducing the orbital
polarization in the p symmetric states. We also discuss a simple sum rule
connecting the XMCD spectra with the orbital moment in the p symmetric states.Comment: 5 pages, 5 figures, accepted for publication in Physical Review
THE SPIRAL WAVE INSTABILITY INDUCED BY A GIANT PLANET. I. PARTICLE STIRRING IN THE INNER REGIONS OF PROTOPLANETARY DISKS
We have recently shown that spiral density waves propagating in accretion
disks can undergo a parametric instability by resonantly coupling with and
transferring energy into pairs of inertial waves (or inertial-gravity waves
when buoyancy is important). In this paper, we perform inviscid
three-dimensional global hydrodynamic simulations to examine the growth and
consequence of this instability operating on the spiral waves driven by a
Jupiter-mass planet in a protoplanetary disk. We find that the spiral waves are
destabilized via the spiral wave instability (SWI), generating hydrodynamic
turbulence and sustained radially-alternating vertical flows that appear to be
associated with long wavelength inertial modes. In the interval , where denotes the semi-major axis of the planetary orbit
(assumed to be 5~au), the estimated vertical diffusion rate associated with the
turbulence is characterized by . For the disk model considered here, the diffusion rate is such that
particles with sizes up to several centimeters are vertically mixed within the
first pressure scale height. This suggests that the instability of spiral waves
launched by a giant planet can significantly disperse solid particles and trace
chemical species from the midplane. In planet formation models where the
continuous local production of chondrules/pebbles occurs over Myr time scales
to provide a feedstock for pebble accretion onto these bodies, this stirring of
solid particles may add a time constraint: planetary embryos and large
asteroids have to form before a gas giant forms in the outer disk, otherwise
the SWI will significantly decrease the chondrule/pebble accretion efficiency.Comment: Accepted for publication in the The Astrophysical Journal, 19 pages,
12 figures, 1 tabl
Hot and Diffuse Clouds near the Galactic Center Probed by Metastable H3+
Using an absorption line from the metastable (J, K) = (3, 3) level of H3+
together with other lines of H3+ and CO observed along several sightlines, we
have discovered a vast amount of high temperature (T ~ 250 K) and low density
(n ~ 100 cm-3) gas with a large velocity dispersion in the Central Molecular
Zone (CMZ) of the Galaxy, i.e., within 200 pc of the center. Approximately
three fourths of the H3+ along the line of sight to the brightest source we
observed, the Quintuplet object GCS 3-2, is inferred to be in the CMZ, with the
remaining H3+ located in intervening spiral arms. About half of H3+ in the CMZ
has velocities near ~ - 100 km s-1 indicating that it is associated with the
180 pc radius Expanding Molecular Ring which approximately forms outer boundary
of the CMZ. The other half, with velocities of ~ - 50 km s-1 and ~ 0 km s-1, is
probably closer to the center. CO is not very abundant in those clouds. Hot and
diffuse gas in which the (3, 3) level is populated was not detected toward
several dense clouds and diffuse clouds in the Galactic disk where large column
densities of colder H3+ have been reported previously. Thus the newly
discovered environment appears to be unique to the CMZ. The large observed H3+
column densities in the CMZ suggests an ionization rate much higher than in the
diffuse interstellar medium in the Galactic disk. Our finding that the H3+ in
the CMZ is almost entirely in diffuse clouds indicates that the reported volume
filling factor (f ≥ 0.1) for n ≥ 104 cm-3 clouds in the CMZ is an
overestimate by at least an order of magnitude.Comment: 33 pages, 5 figures, 3 table
Inner Rim of A Molecular Disk Spatially Resolved in Infrared CO Emission Lines
We present high-resolution infrared spectroscopy of the Herbig Ae star HD
141569 A in the CO v=2-1 transition. With the angular resolution attained by
the adaptive optics system, the gas disk around HD 141569 A is spatially
resolved down to its inner-rim truncation. The size of the inner clearing is
11+-2 AU in radius, close to the gravitational radius of the star. The rough
coincidence to the gravitational radius indicates that the viscous accretion
working together with the photoevaporation by the stellar radiation has cleared
the inner part of the disk.Comment: 6 pages, 3 figures, Accepted for publication in the Astrophysical
Journa
The Structure of Pre-transitional Protoplanetary Disks I: Radiative Transfer Modeling of the Disk+Cavity in the PDS 70 system
Through detailed radiative transfer modeling, we present a disk+cavity model
to simultaneously explain both the SED and Subaru H-band polarized light
imaging for the pre-transitional protoplanetary disk PDS 70. Particularly, we
are able to match not only the radial dependence, but also the absolute scale,
of the surface brightness of the scattered light. Our disk model has a cavity
65 AU in radius, which is heavily depleted of sub-micron-sized dust grains, and
a small residual inner disk which produces a weak but still optically thick NIR
excess in the SED. To explain the contrast of the cavity edge in the Subaru
image, a factor of ~1000 depletion for the sub-micron-sized dust inside the
cavity is required. The total dust mass of the disk may be on the order of 1e-4
M_sun, only weakly constrained due to the lack of long wavelength observations
and the uncertainties in the dust model. The scale height of the
sub-micron-sized dust is ~6 AU at the cavity edge, and the cavity wall is
optically thick in the vertical direction at H-band. PDS 70 is not a member of
the class of (pre-)transitional disks identified by Dong et al. (2012), whose
members only show evidence of the cavity in the millimeter-sized dust but not
the sub-micron-sized dust in resolved images. The two classes of
(pre-)transitional disks may form through different mechanisms, or they may
just be at different evolution stages in the disk clearing process.Comment: 28 pages (single column), 7 figures, 1 table, ApJ accepte
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